Thin film type liquefied natural gas composite enclosure structure and assembly method thereof

Abstract

The invention discloses a film type liquefied natural gas composite enclosure structure which comprises a main screen wall, a main shielding layer, a composite secondary screen wall and a secondary shielding layer which are connected layer by layer, the main shielding layer and the secondary shielding layer are made of first porous materials, and the first porous materials of the main shielding layer and the secondary shielding layer are connected with plywood respectively. The main shielding layer, the composite secondary shielding wall and the secondary shielding layer are connected through low-temperature glue, the main shielding wall is a corrugated metal plate, a plywood of the main shielding layer is pasted with a non-metal connecting piece, and the non-metal connecting piece is connected with the corrugated metal plate through the low-temperature glue. The invention further provides an assembly method of the thin film type liquefied natural gas composite enclosure structure. The strength of the enclosure structure is improved, heat conduction and heat leakage of the connecting pieces are reduced, and the construction difficulty is lowered.

Description

Technical Field

[0001] The present invention relates to the technical field of liquefied natural gas transportation, and in particular to a film-type liquefied natural gas composite enclosure structure and an assembly method thereof. Background Art

[0002] Liquefied natural gas (LNG), a key clean energy source in the global energy transition, faces a core challenge in storage and transportation technology: ensuring safe, efficient, and economical storage and transportation in ultra-low temperatures (-163°C). LNG carriers, the primary vehicle for international LNG trade, rely heavily on the performance of their containment systems to directly impact their operational efficiency, safety, and economic viability. These containment systems must possess extremely low thermal conductivity to suppress LNG evaporation, high strength to withstand the dynamic loads of sloshing liquid cargoes, and high reliability to withstand the long-term challenges of complex marine environments. However, current mainstream containment systems face significant challenges in achieving technological maturity and industrial application, necessitating breakthroughs through structural innovation and material optimization. The LNG containment system, in direct contact with LNG, is a core component of LNG carriers. Currently, membrane-type cargo tanks dominate due to their advantages, including the lack of independent support structures, high tank capacity utilization, and low construction cost. These tanks are primarily categorized into the NO.96 series and the Mark III series. Their typical structure includes a primary shielding layer, a secondary shielding layer, a primary insulation layer, and a secondary insulation layer. Existing membrane-type containment systems usually adopt a layered installation process of secondary insulation layer, secondary membrane layer, main insulation layer, and main membrane layer. The secondary insulation layer is fixed to the hull structure by epoxy resin bonding or anchoring.

[0003] The containment system of an LNG carrier has multiple key functions, as follows. Thermal insulation performance: Reduce the heat exchange between LNG and the environment, control the evaporation rate (BOR, Boil-Off Rate) to below 0.1% / day, and avoid energy waste and increased carbon emissions due to gasification losses. Structural strength: Withstand the instantaneous impact load (up to 200kPa or more) caused by the sloshing of liquid cargo to prevent structural fatigue cracking. Safety barrier: Through the design of primary and secondary double-layer shielding layers, ensure that the sealing can still be maintained when a single layer fails, and avoid the risk of explosion caused by LNG leakage. Economic efficiency: Improve the comprehensive competitiveness of LNG transportation by optimizing tank capacity utilization and reducing construction and maintenance costs. The LNG containment system must meet the "zero leakage" standard and have a design life of at least 25 years. Therefore, technological innovation of the containment system has become a key research direction in the global shipbuilding industry and energy field. There are also many related research and designs. For example, a system for LNG ships and their membrane enclosures adds a supporting wooden structure to the secondary barrier layer to enhance the stability of the structure, but there may be an increased risk of heat leakage. A membrane-type enclosure system and an LNG ship using this system replace the secondary barrier layer with a metal corrugated plate that is the same as the primary barrier layer to enhance the structural strength of the secondary barrier layer. However, this improvement increases the difficulty of structural construction and also increases the overall heat leakage of the structure. It can be seen that the structural strength of the secondary barrier layer is an important direction for improving the enclosure structure of LNG transport ships. In addition, a working platform suitable for the installation of LNG ship cargo hold enclosure systems consists of a 10-level main structure consisting of multiple columns, multiple crossbeams, and multiple longitudinal beams. Support legs of different structures are connected to the ends of each level, and rectangular tubular telescopic beams are installed at the ends of the crossbeams or longitudinal beams of each level. It can be seen that the existing LNG enclosure structure has complex installation processes during installation and there is room for improvement. This is also an important direction for the development and improvement of LNG enclosure systems.

[0004] In summary, one of the core technologies of LNG carriers is the design and manufacture of the containment system. The current mainstream membrane-type containment system has the following problems. Significant heat conduction and heat leakage: The metal connectors used for fixing in the containment structure directly penetrate the insulation layer, forming a thermal bridge between the cold-end liquid tank and the hot-end environment. The thermal conductivity is high, resulting in the transfer of cold to the hull and an increase in the evaporation rate. The secondary shielding layer has low structural strength: The thickness of the secondary shield layer in the containment structure is small, and usually uses Invar steel or glass fiber-aluminum foil-glass fiber composite structure, which has low structural strength and fatigue resistance. Complex installation process: The current mainstream containment structure usually uses through-type metal connectors or overall glue coating for fixed connection. The construction process is complicated and installation is difficult. The prefabricated modules need to be glued and fixed with pressure strips on site. The process is cumbersome and precision control is difficult.

[0005] Therefore, those skilled in the art are committed to providing a thin-film liquefied natural gas composite enclosure structure and an assembly method thereof, so as to improve the strength of the enclosure structure, reduce heat conduction and heat leakage of connectors, and reduce construction difficulty. Summary of the Invention

[0006] In view of the defects in the prior art, the technical problem to be solved by the present invention is how to provide a membrane-type liquefied natural gas containment structure and an assembly method thereof.

[0007] To achieve the above-mentioned objectives, the present invention provides a thin-film type liquefied natural gas composite enclosure structure, comprising a main screen wall, a main shielding layer, a composite secondary screen wall, and a secondary shielding layer connected layer by layer, wherein the main shielding layer and the secondary shielding layer are made of a first porous material, and the first porous materials of the main shielding layer and the secondary shielding layer are respectively connected with plywood, and the layers of the main shielding layer, the composite secondary screen wall, and the secondary shielding layer are connected with low-temperature glue, the main screen wall is a corrugated metal plate, and the plywood of the main shielding layer is glued with non-metallic connectors, and the non-metallic connectors are connected to the corrugated metal plate by low-temperature glue.

[0008] Preferably, the peak height of the corrugated metal plate is 8-12 mm, the wave pitch is 50-80 mm, and the thickness of the corrugated metal plate is 0.8-1.2 mm.

[0009] Preferably, the main screen wall is made of SUS304L material, and a chemical passivation layer is provided on the surface of the main screen wall, and the thickness of the passivation layer is 5-10 μm.

[0010] Preferably, the low-temperature adhesive is an epoxy-polyurethane mixed adhesive, and the coating thickness of the low-temperature adhesive is 0.3-0.5 mm.

[0011] Preferably, the thermal conductivity of the first porous material is 0.018-0.024 W / (m·K), the thickness of the primary shielding layer is 100-150 mm, and the thickness of the secondary shielding layer is 170-300 mm.

[0012] Preferably, the composite secondary screen is formed by stacking aluminum foil-glass fiber woven layer-aluminum foil, and the surface of the aluminum foil is anodized.

[0013] Preferably, the thickness of the plywood is 10-15 mm, the moisture content of the plywood is less than 8%, and the thermal conductivity of the plywood is 0.11-0.14 W / (m·K).

[0014] Preferably, the enclosure structure is block-shaped, corner mounting holes are provided on the corners of the enclosure structure, side mounting holes are provided on the long sides of the enclosure structure, and adjacent enclosure structures are fixed using connectors made of polyetheretherketone reinforced carbon fiber composite material.

[0015] Preferably, gaps are provided between adjacent enclosure structures, and the gaps are filled with a second porous material.

[0016] The present invention also provides an assembly method of a thin-film liquefied natural gas composite enclosure structure, comprising the following steps:

[0017] The main screen wall, composite secondary screen wall, primary shielding layer, secondary shielding layer and plywood are prefabricated in the factory and integrated and installed in a constant temperature workshop;

[0018] Positioning the containment structure modules on the hull;

[0019] Fix and connect the modules of the enclosure structure;

[0020] Carry out air tightness test on the connected enclosure structure.

[0021] The present invention has at least the following beneficial technical effects:

[0022] The thin-film liquefied natural gas composite containment structure of the present invention adopts a multi-layer composite structure design for the secondary shielding layer, combining the synergistic effect of metal and polymer materials to significantly improve the overall mechanical properties; compared with traditional single-layer metal or glass fiber structures, this composite layer exhibits excellent deformation resistance under liquid cargo sloshing loads, can effectively inhibit the occurrence and expansion of fatigue cracks, and ensure long-term service stability.

[0023] The present invention completely blocks the heat conduction path formed by traditional metal penetrations through the comprehensive application of non-metallic connectors and low-temperature bonding technology; the connectors are made of low-thermal conductivity composite materials, combined with an optimized design of the bonding interface, which significantly reduces heat transfer in the vertical direction, thereby reducing the overall heat leakage rate of the system and meeting the stringent insulation performance requirements of LNG storage and transportation.

[0024] The prefabricated modules of the present invention complete the integrated assembly of the primary and secondary shielding layers and the insulation layer in the factory, and the standardized design greatly reduces the complexity of on-site construction; the modules are connected by non-metallic connectors and filled with sealant to achieve rapid splicing, significantly shortening the dock construction period, while reducing the risk of manual operation errors and ensuring installation accuracy and airtightness.

[0025] The concept, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings to fully understand the purpose, characteristics and effects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 1 is a schematic elevation view of a membrane-type liquefied natural gas composite enclosure structure according to an embodiment of the present invention;

[0027] Figure 2 is a three-dimensional schematic diagram of a membrane-type liquefied natural gas composite enclosure structure according to an embodiment of the present invention;

[0028] Figure 3 Schematic diagram of the mounting holes of the enclosure structure according to an embodiment of the present invention.

[0029] In the figure,

[0030] 1-Main screen, 2-Main shielding layer, 3-Composite secondary screen, 4-Secondary shielding layer, 5-Plywood, 6-Resin strip, 7-Hull plate, 8-Second porous material, 9-Connecting bolts, 10-Cutting seam, 11-Fixed connector, 12-Side connection hole, 13-Corner connection hole, 14-Corner connection matrix, 15-Side connection matrix, 16-Corner connector, 17-Bolt hole. DETAILED DESCRIPTION

[0031] The following describes preferred embodiments of the present invention to make its technical content clearer and easier to understand. The present invention can be embodied in many different forms of embodiments, and the scope of protection of the present invention is not limited to the embodiments mentioned herein.

[0032] In the drawings, components with identical structures are denoted by the same reference numerals, and components with similar structures or functions are denoted by similar reference numerals. The size and thickness of each component shown in the drawings are arbitrary and are not limited by the present invention. For clarity, the thickness of components in some places in the drawings is appropriately exaggerated.

[0033] The present invention provides a thin-film liquefied natural gas composite enclosure structure, which uses composite materials and connectors to fix modules, thereby enhancing the overall structural strength and fatigue resistance, reducing heat conduction and heat leakage, and reducing construction difficulty and saving construction costs.

[0034] like Figure 1 As shown, the thin-film liquefied natural gas composite enclosure structure of this embodiment is composed of a main screen wall 1, a main shielding layer 2, a composite secondary screen wall 3, and a secondary shielding layer 4 layered in sequence. The main screen wall 1, the main shielding layer 2, the composite secondary screen wall 3, and the secondary shielding layer 4 are bonded and fixed in sequence by low-temperature glue.

[0035] The main screen wall 1 constitutes the inner wall of the storage tank, plays the role of isolating the cryogenic liquid, and directly assumes the function of isolating the cryogenic LNG liquid from the external environment. The main screen wall 1 of this embodiment adopts corrugated metal plates to meet the requirements of low-temperature sealing, resistance to dynamic loads and thermal insulation assistance. Specifically, the corrugated metal plate is made of SUS304L stainless steel, and a chemical passivation layer is processed on the surface to reduce the risk of stress corrosion in a low-temperature environment. The thickness of the passivation layer is 5-10μm. The peak height of the corrugated metal plate is 8-12mm, the wave pitch is 50-80mm, and the corrugations are arranged longitudinally along the hull to enhance the ability to resist liquid cargo sloshing; the thickness of the metal plate is 0.8-1.2mm, and the corrugated structure increases the equivalent bending stiffness by 40%; laser welding is used between adjacent corrugations, and the weld width is less than or equal to 1mm to ensure sealing.

[0036] The primary shielding layer 2 and secondary shielding layer 4 are constructed from a first porous material. Plywood is attached to the first porous material of each of the primary and secondary shielding layers 5. Within the primary shielding layer 2, the top of the plywood is connected to the primary screen 1, and the bottom is bonded to the first porous material using low-temperature adhesive. Within the secondary shielding layer 4, the top of the plywood 5 is bonded to the first porous material using low-temperature adhesive. In this embodiment, the thermal conductivity of the first porous material is 0.018-0.024 W / (m·K). The thickness of the primary shielding layer 2 is 100-150 mm, and the thickness of the secondary shielding layer 4 is 170-300 mm.

[0037] In this embodiment, non-metallic connectors that meet structural strength requirements are glued onto the plywood on top of the main shielding layer 2 , and the non-metallic connectors are then glued to the corrugated metal plates of the main screen wall 1 .

[0038] The composite secondary shield 3 is formed by stacking aluminum foil, a fiberglass braid, and aluminum foil, then hot-pressing at 80°C, a pressure of 0.5 MPa, and a holding time of 30 minutes. The thicknesses of the layers are 0.1 mm, 0.5 mm, and 0.1 mm, respectively, and the warp and weft density of the fiberglass braid is 60 x 50 strands / cm. After hot-pressing, the interface is strengthened and the aluminum foil surface is anodized to a thickness of approximately 2 μm. The composite secondary shield 3 of this embodiment is gas-tight, preventing gas exchange between the primary shielding layer 2 and the secondary shielding layer 4.

[0039] The thickness of the plywood is 10-15mm, the moisture content is less than 8%, and the thermal conductivity is 0.11-0.14W / (m·K). The plywood has high structural strength to meet the requirements of natural gas maintenance structures.

[0040] Low-temperature adhesive is used to securely connect the primary screen 1 and primary shielding layer 2, the composite secondary screen 3 and secondary shielding layer 4, and the different insulation materials within the primary shielding layer 2 and the secondary shielding layer 4. The low-temperature adhesive is an epoxy-polyurethane hybrid adhesive with a coating thickness of 0.3-0.5mm.

[0041] A resin strip 6 is provided at the bottom of the plywood 5 of the secondary shielding layer 4, through which the enclosure structure is mounted on the hull plate 7. The resin strip 6 and the hull plate 7 are fixed by low-temperature glue to avoid heat leakage.

[0042] like Figure 2 As shown, the enclosure structure of this embodiment is a block-shaped modular structure, and the modules are spliced into an integral structure and then installed on the hull plate 7. Each module is provided with corner connection holes 13 at the four corners and a side connection hole 12 in the middle of the long side. When splicing, adjacent corner connection holes 13 form a corner connection matrix 14; adjacent side connection holes 12 form a side connection matrix 15. The corner connection matrix 14 is connected by a four-hole connector, and the side connection matrix 15 is connected by a double-hole connector. The connector uses polyetheretherketone (PEEK) reinforced carbon fiber composite material with a thermal conductivity of 0.25W / (m·K). The module is fixed by a short-size connector of non-metallic composite material to avoid heat leakage caused by the thermal bridge effect caused by the through-type metal connector.

[0043] like Figure 3 As shown, in the specific embodiment of the four-hole connector, a bolt hole 17 is provided on the corner connector 16, the bolt has a diameter of 8-12 mm and a length of 30-50 mm; the thickness of the corner connector 16 is 3-5 mm.

[0044] Each enclosure module is prefabricated with corresponding connector mounting holes. During assembly, adjacent module connector holes are butted together. At corners, the corner connector holes 13 of four adjacent modules are butted together to form a square matrix of connector holes. Non-metallic connectors with corresponding openings are placed in these holes, and non-metallic bolts are then installed through these holes. Non-metallic bolts are installed in all four holes to secure the connectors to the modules. In non-corner areas, two side connector holes 12 are butted together to form a rectangular matrix. Rectangular non-metallic connectors with corresponding openings are placed in these holes, and non-metallic bolts are then installed through these holes. Non-metallic bolts are installed in both holes to secure the connectors to the modules.

[0045] A gap of 20-30mm is left between adjacent enclosure structure modules to relieve the structural stress caused by thermal expansion and contraction and swaying of the hull during operation. Figure 1 As shown, the second porous material 8 is filled in the gap. The second porous material 8 is a flexible porous material with a thermal conductivity of 0.033-0.042 W / (m·K). During operation, the deformation caused by its own flexibility can relieve structural stress and ensure structural safety.

[0046] like Figure 1As shown, after modular connection, adjacent primary shielding layers 2 are separated by cut seams 10. Adjacent composite secondary shields 3 are connected by connecting bolts 9 and fixing connectors 11. These connecting bolts 9 and fixing connectors 11 form a corner connection matrix 14 or a side connection matrix 15. To ensure airtightness, the primary shield 1 is a monolithic structure and is installed after the modules are assembled.

[0047] The present invention also provides an assembly method for a thin-film liquefied natural gas composite enclosure structure, the specific process of which is as follows:

[0048] The main screen wall, composite secondary screen wall, primary shielding layer, secondary shielding layer and plywood are prefabricated in the factory and integrated and installed in a constant temperature workshop (20±2℃). The module size tolerance is ±1mm.

[0049] The hull positioning laser positioning system positions and installs the module, and the positioning error between the module and the hull plate is ≤1.5mm;

[0050] Module splicing: modules are fixedly connected with each other, with a non-metallic bolt pre-tightening force of 20-25 N·m, and gaps filled with a second porous material and low-temperature silica gel (thermal conductivity 0.2 W / (m·K));

[0051] Air tightness test, helium leak detection rate ≤1×10 -6 mbar·L / s, pressure holding time ≥24h.

[0052] The thin-film liquefied natural gas composite enclosure structure of the present invention adopts a multi-layer composite structure design for the secondary shielding layer, which combines the synergistic effect of metal and polymer materials to significantly improve the overall mechanical properties; compared with traditional single-layer metal or glass fiber structures, the composite layer shows excellent deformation resistance under liquid cargo sloshing loads, which can effectively inhibit the occurrence and expansion of fatigue cracks and ensure long-term service stability. Through the comprehensive application of non-metallic connectors and low-temperature bonding technology, the heat conduction path formed by traditional metal penetrations is completely blocked; the connectors adopt low thermal conductivity composite materials, combined with the optimized design of the bonding interface, which significantly reduces the heat transfer in the vertical direction, thereby reducing the overall heat leakage rate of the system and meeting the stringent requirements of LNG storage and transportation on insulation performance. The prefabricated modules complete the integrated assembly of the primary and secondary shielding layers and the insulation layer in the factory, and the standardized design greatly reduces the complexity of on-site construction; the modules are connected by non-metallic connectors and filled with sealants to achieve rapid splicing, which significantly shortens the dock construction period, while reducing the risk of manual operation errors and ensuring installation accuracy and airtightness.

[0053] The secondary shielding layer composite material of this invention utilizes a sophisticated lamination and heat curing process to ensure strong and uniform interfacial bonding between the layers. Non-metallic connectors are mass-produced through injection molding, ensuring high process stability. The modular assembly process is compatible with existing shipbuilding production lines, enabling large-scale deployment without requiring additional equipment modifications. Prefabricated modules undergo rigorous airtightness testing and mechanical property testing before shipment to ensure each module meets design requirements. During on-site installation, a digital positioning system monitors module assembly accuracy in real time, minimizing operator error.

[0054] The above describes in detail the preferred embodiments of the present invention. It should be understood that those skilled in the art can make numerous modifications and variations based on the concepts of the present invention without inventive effort. Therefore, any technical solutions that can be derived by those skilled in the art through logical analysis, reasoning, or limited experimentation based on the concepts of the present invention and the prior art should be within the scope of protection defined by the claims.

Claims

1. A membrane type liquefied natural gas composite enclosure structure, characterized in that: It includes a main screen wall, a main shielding layer, a composite secondary screen wall, and a secondary shielding layer that are connected layer by layer. The main shielding layer and the secondary shielding layer are made of a first porous material. The first porous materials of the main shielding layer and the secondary shielding layer are respectively connected with plywood. The main shielding layer, the composite secondary screen wall, and the secondary shielding layer are connected with low-temperature glue. The main screen wall is a corrugated metal plate. The plywood of the main shielding layer is glued with non-metallic connectors. The non-metallic connectors are connected to the corrugated metal plate through low-temperature glue.

2. The thin film type liquefied natural gas composite enclosure structure according to claim 1, characterized in that: The crest height of the corrugated metal plate is 8-12 mm, the wave pitch is 50-80 mm, and the thickness of the corrugated metal plate is 0.8-1.2 mm.

3. The thin film type liquefied natural gas composite enclosure structure according to claim 1, characterized in that: The main screen wall is made of SUS304L material. A chemical passivation layer is provided on the surface of the main screen wall. The thickness of the passivation layer is 5-10 μm.

4. The thin film type liquefied natural gas composite enclosure structure according to claim 1, characterized in that: The low-temperature adhesive is an epoxy-polyurethane mixed adhesive, and the coating thickness of the low-temperature adhesive is 0.3-0.5 mm.

5. The thin film type liquefied natural gas composite enclosure structure according to claim 1, characterized in that: The thermal conductivity of the first porous material is 0.018-0.024 W / (m·K), the thickness of the primary shielding layer is 100-150 mm, and the thickness of the secondary shielding layer is 170-300 mm.

6. The thin film type liquefied natural gas composite enclosure structure according to claim 1, characterized in that: The composite secondary screen is formed by stacking aluminum foil, glass fiber braided layer and aluminum foil, and the surface of the aluminum foil is anodized.

7. The membrane type liquefied natural gas composite enclosure structure according to claim 1, characterized in that: The thickness of the plywood is 10-15 mm, the moisture content of the plywood is less than 8%, and the thermal conductivity coefficient of the plywood is 0.11-0.14 W / (m·K).

8. The membrane type liquefied natural gas composite enclosure structure according to claim 1, characterized in that: The enclosure structure is block-shaped, with corner mounting holes provided on the corners of the enclosure structure and side mounting holes provided on the long sides of the enclosure structure. Adjacent enclosure structures are fixed using connectors made of polyetheretherketone reinforced carbon fiber composite material.

9. The membrane type liquefied natural gas composite enclosure structure according to claim 8, characterized in that: Gaps are provided between adjacent enclosure structures, and the gaps are filled with a second porous material.

10. The assembly method of the membrane type liquefied natural gas composite enclosure structure is characterized in that: The following steps are involved: The main screen wall, composite secondary screen wall, primary shielding layer, secondary shielding layer and plywood are prefabricated in the factory and integrated and installed in a constant temperature workshop; Positioning the containment structure modules on the hull; Fix and connect the modules of the enclosure structure; Carry out air tightness test on the connected enclosure structure.

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